Iraqi oil production was hugely diminished as a result of the war. That caused the world price to rise, along with profits for Big Oil. The goal of Juniorbush's takeover of Iraq was to turn it into a sort of US puppet regime. Cheney sent in droves of rightwing fanatics, and they designed a new Iraqi Constitution and flag. It was a disaster, because Iraq was a country with a Shia majority in which Shia Muslims were given lower class status. And of course, many Iraqi Shiites identified very strongly with Iran, also a Shia nation.
The facts about religion and the history of Iraq was not taken into account by the wannabe puppetmasters and the Juniorbush plan was scrapped.
The Sunnis comprised the civil service, the army and the police of Iraq, and were loyal to Saddam's Baathist party, They were thrown out of work, but many of them knew where the arms were stored and who would pay for them both in Iraq and in Syria, which was having its own civil war at they time.
Big Oil profited greatly from Juniorbush's war. As did the Saudis and the Russians.